This invention is generally directed to developer compositions, and more specifically the present invention is directed to the incorporation of specific carrier particles into developer compositions. Therefore, in one embodiment the present invention is directed to coated carrier particles having incorporated therein colorless components, such as certain metal halides, primarily for the purpose of achieving a specific conductivity value range for the aforementioned particles. In one embodiment of the present invention, the developer compositions are comprised of toner resin particles, pigment particles, carrier particles with a coating thereover such as those selected from polymeric compositions especially those derived from vinyl homopolymers and copolymers, and incorporated into the coating specific metal halides. The aforementioned developer compositions, which are particularly useful in electrophotographic imaging processes, provide developers which substantially eliminate contamination of the imaging apparatus within which they are incorporated; and also these compositions have desirable conductivity values and excellent charge admixing times.
The xerographic process involves the development of latent images by developer compositions comprised of toner resin particles, pigment particles, and carrier particles. Numerous different developer compositions are described in the prior art, inclusive of those with toner resin particles comprised of styrene acrylate copolymers, styrene butadiene copolymers, styrene methacrylate copolymers, polyesters, and the like. Additionally, there is disclosed in the prior art the selection of various carrier particles, both coated and uncoated, for use as a component in a developer composition. Moreover, it is known that charge enhancing additives can be incorporated into various developer compositions for the purpose of imparting the desired charge polarity to the toner resin particles.
There are disclosed in U.S. Pat. No. 3,795,617 carrier particles containing magnetically attractable core particles with a resinous vinylidene chloride copolymer coating thereon. Illustrative examples of copolymeric materials selected are outlined in column 5, beginning at line 4, and include, for example vinylidene chloride, acrylonitrile, and acrylic acid terpolymers. Additionally, it is indicated in this patent that useful results can be obtained by substituting one or more alkyl esters of acrylic or methacrylic acid for the acrylonitrile component of the copolymer, which esters typically have from about 1 to 18 carbon atoms in the alkyl group, inclusive of methyl methacrylate, ethyl methacrylate, and butyl methacrylate.
Further, there are disclosed in U.S. Pat. No. 4,310,611 novel magnetic carrier components comprised of a mass of passivated particles of magnetic stainless steel with a thin tightly adherent chromium rich layer. It is indicated in column 2, beginning at line 35 of this patent, that optionally the passivated particles can have a coating of a resin which aids in the triboelectrical charging of the toner, but which is discontinuous or thin enough to allow the particle mass to remain conductive. Also, examples of resins selected as carrier coatings include those described in U.S. Pat. Nos. 3,795,617; 3,795,618; and 4,076,857. Specific examples of carrier coatings listed in column 4 of the U.S. Pat. No. 3,795,617 include fluorocarbon polymers such as polytetrafluoroethylene, polyvinylidene fluoride, and polyvinylidenefluoride-co-tetrafluoroethylene.
In U.S. Pat. No. 4,374,192 there are disclosed novel carrier coatings with miscible mixtures of a butadiene acrylonitrile rubber, and containing from about 20 percent to about 40 percent of acrylonitrile together with a polyurethane elastomer. These coatings, according to the teachings of this patent, are tough, tenacious, and not tacky, reference the disclosure in column 4, beginning at line 3.
Many other patents are in existence disclosing toner and carrier particles, representative of which include U.S. Pat. No. 4,051,077, relating to developer compositions with various additives; U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, which discloses positively charged developer compositions comprised of resin particles, pigment particles, alkyl pyridinium charge enhancing additives, and carrier particles; U.S. Pat. No. 3,627,522, the disclosure of which is totally incorporated herein by reference, directed to developer compositions with carrier particles coated with terpolymer resins of styrene, methylmethacrylate, and an organo silane; U.S. Pat. No. 3,923,503, the disclosure of which is totally incorporated herein by reference, disclosing methods of imaging with developer compositions comprised of steel carrier particles coated with various resins, such as polymethylmethacrylate, polyvinylidene fluoride, and terpolymers of styrene; and U.S. Pat. No. 3,526,533, the disclosure of which is totally incorporated herein by reference, directed to carriers with coatings of linear addition copolymers of polymerized polystyrene, polymerized acrylates, or polymerized methacrylates, and polymerizable organo silicon compositions.
Of particular interest with respect to the invention of the present application are the carrier particles illustrated in U.S. Pat. No. 3,533,835, the disclosure of which is totally incorporated herein by reference, which particles are comprised of a core with a coating thereover, and wherein the coating contains therein numerous conductive substances such as silver iodide, which iodide decomposes into an undesirable black color as contrasted to copper iodide which is colorless, and does not decompose. While the substances of the U.S. Pat. No. 3,533,835 are suitable for their intended purposes, they generally are not colorless as is the situation with the additive incorporated into the carrier coatings of the present invention; and furthermore, with the invention of the present application, there are enabled other advantages such as avoiding contamination of the imaging apparatus, excellent admixing times in some embodiments, and acceptable conductivity values.
Also of interest are U.S. Pat. No. 4,133,933, which discloses electrosensitive recording sheets in which cupric iodide is selected as an electroconductive material, which iodide particles can be whitened by an aqueous akaline material; U.S. Pat. No. 4,275,103, which discloses an electographic recording sheet wherein metal oxide semiconductors that are virtually colorless are selected, examples of such semiconductors including tin oxide, dye indium trioxide, and zinc oxide; and U.S. Pat. No. 4,601,967 directed to toner particles consisting of an electroconductive core in a coating layer, which coating layer may comprise copper iodide in the form of a powder iron, nickel, cobalt, or manganese, reference for example column 3, lines 3 to 9.
Accordingly, there is a need for developer compositions wherein there are selected carrier coatings having incorporated therein colorless conductive additives. There is also a need for carrier particles that possess desirable conductivity values which are achievable by incorporating into the carrier coatings specific colorless components thereby avoiding color contamination, a problem with some prior art carrier coatings wherein, for example, carbon black is selected as the conductivity controlling component that is incorporated into the carrier coating. In addition, there is a need for developer compositions with carrier coatings having incorporated therein specific colorless conductive components, which compositions maintain their triboelectric charging characteristics for extended time periods.